The internal shells of Autogenous or Semi-Autogenous (SAG) mills used in the mining industry for grinding minerals are fixed to the mantle of the mill by means of bolts which are mainly introduced from the inside of this to pass the mantle of the mill by a perforation. Since the tip of the bolt is outside the mill, it engages a rubber washer, a steel washer and a nut. This operation is usually performed by several operators which use pneumatic tools to remove nuts and washers separately; this involves many hours in performing these three processes considering the size of this type of mills and the large number of fixing elements available. The washers used for fixing the shells of such mills correspond to cup-type washers which are formed by a hollow metal section that accommodates a rubber washer whose function is to make a seal that prevents runoff of fluids from the inside the mill. An example of this type of fastening systems is that disclosed by Patent CA1120966.
Such washers are fixed at the surface of the mill by means of a lock nut so as to provide tight adjustment and capable of withstanding vibrations without rotating, which many time makes it difficult the removal the nut, and then of the washer for replacement of shells.
In many cases, operators must hit the fixing elements to release them and in extreme cases, cutting the nuts with oxy-cutting processes. Additionally, the rubber washers usually remain attached to the locking bolt which implies additional effort on the part of operators to extract these elements often making use of specialized tools not for it.
In the state of the art there are solutions that have tried to solve the problem of extracting nuts and washers of mill shells. An example of this is disclosed by the Patent Application CL 3069-2008 that proposes a quick release nut for fasteners of mill shells, without unscrewing it. To this end a nut with notches in the periphery and orthogonal to the flat faces is provided, that allow concentrate stresses when a wedge between themselves is provided. Thus, a crack is created and finally the faces are separated to allow advancement of the crack to rupture and complete separation of the parts.
Although this solution provides a mechanism for quick removal of the nut, it is a complex process and it does not suggest a mechanism for the specific extraction of washers used in this type of fixings as explained above.
Similarly, the Patent Application CL 1886-2011 discloses a nut to be extracted quickly from the fastening bolts of mill lining, plates, which consists of a hollow hexagonal outer body and an inner cylindrical body constituted by a bushing divided with internal thread. For loosening of the nut a pneumatic or hydraulic tool is used to eject the outer hexagonal body; then, the inner cylindrical body which is threaded onto the bolt is struck with a smaller tool such as a hammer, so that to open the two split halves, with the nut and bolts becoming released.
Again, the solution provided does not suggest a mechanism for extracting the washers used in this type of fastener, which as in the previous case requires the use of additional tools and complex processes for the extraction of the nut.
Furthermore, the utility model application No CL 182-201 discloses an adjustment washer for a fastening system of mills engaged in treating ores known in the market under the name “Elingol”. This adjustment washer mainly consists of a forged steel washer with a drag supportive device which is affixed a metal ear and a hot vulcanized rubber washer adhered to the previous one. The washer is conventionally installed on the bolt to finally tighten the assembly. The removal of the fastening system is made using an impact wrench provided with a die having on its periphery a device that takes the washer and rotates together with the nut outwards.
While this invention allows the extraction of the fastening system faster than conventional systems, it must be done with a specialized tool configured to engage both the nut and the washer. This represents an increase in maintenance costs. In addition, this patent does not mention the insertion mechanism of the washer and nut on the holding bolt which, given the features of the invention, suggests that this process must be done in different steps and with different tools.
Another drawback associated with the inventions mentioned is that the components of the fastening system of shells, namely nut and washer, are provided separately, which may hinder their management and represent a risk when working with them in height, e.g. on scaffolding.
Therefore, after noting the drawbacks observed in the devices related to the present invention and forming part of the state of the art, an object of the present invention is to provide a comprehensive quick removal fastening system for shells and liners of mills, i.e. consisting of a 3 in 1 system, allowing insertion and removal in one step and using a single conventional tool; this speeds up the process of insertion and removal of the fastening systems associated with the maintenance of mills, also increasing the safety of the process.
Another object of the present invention is to provide a fastening system that prevents its unauthorized disassembly for unauthorized repairs, thereby avoiding misuse and possible associated damage.